Design for high density memory with relaxed metal pitch

Abstract

A method and design for stitching polysilicon wordlines to straps formed of interconnected metal line segments formed in two or more metallization levels. Each strap comprises a continuous conductive metal line passing alternatively from one metal layer to another in a selected sequence. The sequence of segments in each strap alternates in phase with the sequence in next nearest neighbor straps but may be in phase with second nearest neighbor straps. Thereby the pitch of strap segments on each metallization level is at least twice that of the subjacent polysilicon wordlines. The total length of each metal in each strap is the same in all straps. This arrangement allows the use of metals having different resistivities in each strap with all the straps having identical overall resistance. The metals used in the two or more levels may also have different minimum design rules without compromising the identical overall performance of all the straps. In a second embodiment a method and design is described for doubling the length of polysilicon sub-wordlines in a sub-wordline memory array without reducing performance by connecting sub-wordline to sub-wordline decoders by metal straps connected to the sub-wordlines midpoints.

What is claimed is: 
     
       1. An integrated circuit memory comprising: (a) an array of memory cells arranged in rows and columns;   (b) a plurality of wordlines each connected to plural cells in at least one respective row of said array;   (c) a plurality of bitlines each connected to plural cells in at least one respective row of said array;   (d) peripheral device circuits comprising wordline decoders located on opposite sides of said array; and   (e) metal straps formed over said wordlines on an insulative layer running parallel with said wordlines and connected along their length to said wordlines by a plurality of metal contacts and at their ends to said wordline decoders;   wherein said metal straps comprise an alternating sequence of serially interconnected metal line segments in at least two metallization levels, with interconnections formed through openings in an insulative layer separating said metallization levels;   wherein said alternating sequence is reversed in phase between next adjacent metal straps such that on each respective metallization level, line segments become line gaps and line gaps become line segments;   wherein at least one of said at least two metallization levels is formed over a globally planarized insulation layer; and   wherein said metal straps are connected at their ends to said wordline decoders on opposite sides of said array in an alternating sequence by a line segment formed in one of said at least one of said at least two metallization levels formed over said globally planarized insulation layer.   
     
     
       2. The integrated circuit memory of claim 1 wherein said at least two metallization levels are comprise of different metals. 
     
     
       3. The integrated circuit memory of claim 1 wherein one of said at least two metallization levels is tungsten. 
     
     
       4. The integrated circuit memory of claim 1 wherein one of said at least two metallization levels is selected from the group consisting of aluminum, an aluminum alloy, copper, and a copper alloy. 
     
     
       5. An integrated circuit memory sub-wordline section comprising: (a) an array of memory cells arranged in rows and columns;   (b) a plurality of wordlines each connected to plural cells in at least one respective row of said array;   (c) a plurality of bitlines each connected to plural cells in at least one respective row of said array;   (d) peripheral device circuits comprising sub wordline decoders located on opposite sides of said array; and   (e) metal straps formed over said sub-wordlines on an insulative layer running parallel with said wordlines and connected at one end to the midpoints of said sub-wordlines and at the other end to said sub-wordline decoders;   wherein said metal straps are formed over a globally planarized insulation layer;   wherein said metal straps are connected at their ends to said sub-wordline decoders on opposite sides of said array in an alternating sequence whereby in accordance with said alternating sequence, said metal straps possess a pitch which is twice that of said sub-wordlines.   
     
     
       6. The integrated circuit memory sub-wordline section of claim 5 wherein said metal straps are selected from the group consisting of aluminum, an aluminum alloy, copper, and a copper alloy.